Charcoal having encapsulated igniter material

ABSTRACT

The properties of charcoal can be improved by providing microcapsules containing an ignitable material on or within the charcoal. The microcapsules can be made of polyacrylate and the ignitable material includes hydrocarbons such as a paraffin combination, alcohols, and combinations.

BACKGROUND OF THE INVENTION

Charcoal has long been used as a fuel especially for cooking. Lightingthe charcoal, however, can be problematic. A typical match flame lackssufficient heat to ignite or burn the charcoal. Accordingly, a commonapproach has been to first pour lighter fluid on the charcoal and thenapply a lit match. The match ignites the lighter fluid which in turnignites and burns the charcoal. Several difficulties with this processexist including inconvenience and potential danger in use and storage ofthe flammable lighter fluid. A charcoal that can be more easily lit hasbeen long desired and several inventors have addressed this issue.

For example, U.S. Pat. No. 2,816,013 proposes impregnating charcoal witha liquid hydrocarbon such as odorless mineral spirits and then coatingwith a coating material such a polyacrylate and/or cellulose nitrates.The polymeric coating should be flammable, relatively impervious toliquid hydrocarbon and produce little smoke or odor during burning. Toimprove the flammability of a polyacrylate coating, a cellulose nitratecan be added. A coating containing 40-50% cellulose nitrate with anitrogen content of 13.41% is considered most suitable.

U.S. Pat. No. 3,395,002 relates to a so-called “instant igniting”charcoal made by impregnating charcoal with an alcohol and polymersolution and then gelling the impregnated solution in situ. The alcoholand polymer solution is typically a small amount of nitro cellulosedissolved in ethyl alcohol. The gelled igniter fluid impregnatedcharcoal can be coated with a suitable flammable polymer such aspolyvinyl alcohol or cellulose acetate (or both coatings) to improvestorage and clean handling. Generally the charcoal contains 20% or 25%of the gelled impregnant to achieve easy lighting.

U.S. Pat. No. 3,431,093 also relates to “instant-igniting” charcoal. Amixture of saturated higher fatty alcohols (C12-C18) and higher fattyacids (C12-C18) is impregnated into charcoal. The higher fatty alcoholsand acids are heated to a molten state and the charcoal submergedtherein to impregnate the igniter mixture therein. This mixture issupposed to easily ignite and burn with little smoke and a pleasantodor. Small amounts of nitrocellulose can also be included in the higheralcohol and acid mixture. Generally around 9-10% of the acid and alcoholmixture is needed for good results. The impregnated charcoal mayoptionally be coated.

U.S. Pat. No. 4,165,968 relates to a rapidly ignitable coatingcomposition for charcoal briquettes. The composition is a gelablemixture of a flammable alcohol and a cellulose material that furthercontains expanded perlite. Once the briquettes are coated with the gelcomposition, the temperature is dropped, preferably to −10° F. to −32°F. The cold atmosphere causes the gel to quickly solidify while majoramounts of the alcohol are still suspended. This limits penetration ofthe alcohol into the briquette. The coated briquettes should be storedin an air-tight bag to prevent alcohol from escaping.

U.S. Pat. No. 4,822,380 relates to coated carbonaceous materialsincluding charcoal. The charcoal is first dipped into a flammable liquidsuch as a light kerosene product and then dipped into melted paraffinhaving a higher melting point of around 160° F. The specified paraffinis described as having the right balance of ignition ease and coatingquality. The flammable liquid coating step is reported to reduce theamount of paraffin taken up in the paraffin dip step from 6-7% retentiondown to 3-4% retention resulting in cost savings. The paraffin cancontain additives to provide a white and opaque exterior and colors arealso suggested for achieving desired aesthetics.

Separate from the desire to eliminate the need for lighter fluid, U.S.Pat. No. 4,084,939 is directed to improving the safety or ease in usinglighter fluid. To a gelled alcohol charcoal lighter fluid are addedmicrocapsules of volatile solvent that rupture during the fuel gelburning to provide an audible popping or crackling sound. This soundindicates that the lighter fluid is burning. The microcapsules arepreferably xylene encapsulated in a modified gelatin though kerosenecould also be used. Another suggestion is petroleum distillatesencapsulated in a urea-formaldehyde polymer. To insure that the capsulesrupture, the encapsulating material must not melt at the burningtemperature of the gelled alcohol. The volatile solvent inside themicrocapsule will thus burst the capsule upon heating and produce thedesired popping sound. The alcohol gel typically uses alcohols having1-6 carbon atoms. The alcohol(s) are gelled in a dispersion of ethylene-acrylic acid copolymers.

While many solutions have been proposed, there remains a desire for easylighting charcoal.

SUMMARY OF THE INVENTION

The present invention relates to charcoal having microcapsules ofignitable material thereon. Accordingly, a first aspect of the inventionrelates to a charcoal composition, comprising charcoal and microcapsulesdisposed on the surface thereof or within the charcoal composition,wherein said microcapsules contain an ignitable material. The ignitablematerial is typically, but not necessarily a liquid at room temperatureand includes conventional lighter fluids and/or alcohols. Themicrocapsules can be made of any flammable microcapsule material such asa polyacrylate. The microcapsules can be coated on to the charcoal,especially a briquette, usually with a binder.

Another aspect of the invention relates to a process for making acharcoal composition, which comprises:

-   -   (a) coating charcoal with a slurry comprising a liquid having        microcapsules dispersed therein, said microcapsules containing        an ignitable material, to form a wet coated charcoal; and    -   (b) drying said wet coated charcoal to form charcoal having said        microcapsules disposed on the surface thereof.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the discovery that ignitable materialin a microcapsule can be combined with charcoal and provide improvedlighting characteristics. Additionally, evaporation of the ignitablematerial can be substantially prevented which can improve the storagesafety and effectiveness after storage.

The charcoal used in the present invention can be of any source.Typically the charcoal is derived from wood, but derivations fromvegetable matter or from coal, each alone or in combinations of two ormore, are also included. The charcoal is conveniently in the form of abriquette, a traditional form for use in cooking or grilling. So-called“lump” charcoal can also be used, but the briquette form is generallypreferred for production efficiency.

The ignitable material contained in the microcapsule is any compound ormixtures of compounds that are normally flammable in the presence of amatch flame. Typically the ignitable material comprises at least onehydrocarbon or at least one alcohol, or both, and may further includeother compounds such as carboxylic acids, esters, etc. Generally thehydrocarbons contain 5 to 18 carbon atoms and typically are one or morestraight, branched, or cyclo- alkanes having 5 to 13 carbon atoms. Thealcohols typically have 1 to 13 carbon atoms and 1 to 3 OH groups, moretypically 1-8 carbon atoms with one OH group. Carboxylic acids andesters derived from the aforementioned hydrocarbons or alcohols can alsobe used. Aromatic compounds can be used or present in the ignitablematerial but are usually preferred to be omitted for flavor and/or odorreasons. The ignitable material is usually a liquid at room temperature.But in some embodiments a solid can be used as the ignitable material oras a portion thereof. Examples of ignitable material include commerciallighter fluid, mineral spirits including odorless mineral spirits,petroleum distillates, ethanol, propanol, butanol, etc., andcombinations thereof.

The microcapsules are comprised of a relatively thin wall encapsulatinga core portion. The microcapsules have a size of less than 200 micronsand preferably have a median size or diameter within the range of 1 to30 microns, more typically 5 to 20 microns. Larger microcapsules mayprovide greater amounts of ignitable material (per capsule) but maybecome more prone to accidental rupture during handling or storage.Smaller microcapsules tend to require more wall material for a givenamount of ignitable material and thus can raise cost issues. The aspectratio of the weight of the material encapsulated (the “core”) to theweight of the wall material is generally at least 60%; meaning 60% ormore core material and 40% or less wall material, respectively. For costefficiency reasons, higher aspects ratios are usually preferred, such asat least 70% core material, at least 80% core material, and at least 90%core material. Having too little wall material may eventually lead topremature rupture issues. Typically the wall material is at least 2%more typically at least 3%. A common range is that the core material is80 to 95% of the weight of the capsule. These values are average valuescalculated by techniques known in the microcapsule art.

The microcapsules can be made of any suitable microencapsulatingmaterial. The material should be flammable, such as in the presence of amatch flame, either per se or in combination with the ignitablematerial. Common microcapsule materials include polyacrylate, gelatin,melamine-formaldehyde, and polyurethane. Polyacrylate polymers can beespecially suitable because they can burn readily and provide combustionproducts that are essentially the same as those of wood. Also the widechoice of acrylate monomers allows the wall burning properties to befine-tuned via the glass transition temperature of the chosen monomerand/or monomer blend. For clarity a polymer is considered a polyacrylateif it contains at least 20% acrylate monomers, typically at least 50%acrylate monomers, and often at least 80% acrylate monomers. Gelatinwall-based capsules burn/ignite but can leave more residue than apolyacrylate wall-based capsule. In some applications, noticeablepost-burning capsule residue may be undesirable. It is usually desirablefor a polymeric wall material to be formed from monomers that aresoluble in the ignitable material.

The microcapsules containing the ignitable material can be made bytechniques known in the microencapsulating art. Typically themicrocapsules are formed from monomer(s) via in situ polymerization.Specifically emulsion polymerization is a useful technique. In anoil-in-water emulsion, the polymerization occurs at the interface of thefine droplets of oil phase dispersed in the water or hydrophilic phase.The polymerization results in the oil drops having a polymer wall formedaround them. Either the oil phase or the water phase, or both, cancontain the monomer(s) and the initiator(s) and/or catalysts. In oneembodiment, the dispersed oil phase contains the ignitable material andthe monomer(s) dissolved therein. Initiators or catalysts can optionallybe present in the oil phase as well. The water phase contains aninitiator and optionally additional monomers. The monomers in the oilphase must be dissolved in the oil phase of the ignitable material. Thisincludes, however, heating the oil phase. Thus ignitable material thatwould normally be solid at room temperature but is made liquid or moltenand into which the monomers dissolve can be used. In this way,microcapsules of solid ignitable material can be made; e.g., uponcooling formed microcapsules, the encapsulated ignitable materialbecomes solid.

In some embodiments it is preferred to use a divalent acrylate monomer.The divalent acrylate monomer can comprise at least 20%, typically atleast 50%, and in some embodiments at least 80% of the polymeric wallmaterial. The divalent acrylate monomer can be used as the only acrylatemonomer or part of a mixture of acrylate monomers. Non-acrylate monomerscan also be incorporated. Ethylene dimethacrylate is a useful divalentacrylate monomer and is generally soluble in liquid ignitable materials.The techniques and materials taught in U.S. Pat. No. 7,736,695, which isincorporated herein in its entirety, are suitable for makingmicrocapsules of ignitable material for use in the present invention,provided that an ignitable material is used in the oil phase and theacrylate monomer is soluble in the oil phase, and usually soluble in theignitable material.

Once the microcapsules containing ignitable material are formed they maybe disposed on the surface of the charcoal in various ways. Oneconvenient method involves coating the charcoal with a slurry comprisinga liquid having the microcapsules dispersed therein to form a wet coatedcharcoal; and drying the wet coated charcoal to form charcoal having themicrocapsules disposed on the surface of the charcoal. The coating cancover all surfaces of the charcoal or only a portion such as one majorface or one side. Often the formation of the microcapsules results in anaqueous slurry that can be used to coat the charcoal. The slurry can beconcentrated if desired before coating. Alternatively, the microcapsulescan be recovered from the slurry or other medium in which they wereformed and coated onto the charcoal, optionally after being dispersed ina different solvent or coating material. A binder such as a polymer canbe present in the slurry/coating medium so that upon drying of the wetcoated charcoal, the solvent is removed and microcapsules are dispersedin a binder layer. The recovered microcapsules can also be incorporatedinto the charcoal such as during formation of a briquette, preferablywith a portion of the microcapsules being present at the surface of thecharcoal. In an alternative embodiment, such as with charcoals formedfrom wet pressing powdered carbonaceous materials or otherwisefashioning the briquettes from particulates, the microcapsule slurry isincorporated or included within the particulate mix that forms thecharcoal. The microcapsules containing ignitable material in suchembodiment would be within the charcoal or briquette. Such charcoal canhave microcapsules disposed on or in the charcoal, or both, resulting incharcoal containing microcapsules with ignitable material. In allembodiments where the microcapsules are contained within the charcoal, acoating of microcapsules containing the same or different ignitablematerial can be placed on one or more surfaces of the charcoal.

The microcapsules containing an ignitable material are intended to helpthe lighting characteristics of charcoal. To this end, the amount of theignitable material provided varies depending on cost, efficacy desired,and materials selected. In general the microcapsules provide theignitable material in an amount of 1% to 50%, more typically 2% to 25%,and in some embodiments 3% to 15% based on the weight of the charcoal.Thus for a typical charcoal briquette weighing around 22 grams, theamount of ignitable material is generally in the range of 0.2 grams to11 grams, more typically 0.4 to 5.5 grams. Higher amounts may not bepractical economically and/or from over-flame issues. The use of loweramounts of ignitable material within the above range is generallydesirable from a cost perspective. Also, because the ignitable materialis microencapsulated, the fear of loss of the ignitable material duringstorage by evaporation is diminished, which may facilitate the reliableuse of lesser amounts. Accordingly for a typical charcoal briquette(having a weight of around 20 to 25 grams) the microcapsules may provide0.5 to 7 grams, more typically 0.5 to 3 grams, and in some preferredembodiments 0.5 to 2.5 grams. It is believed that some commerciallighter fluid impregnated charcoal uses 3 grams per briquette. Usingless than that amount would be advantageous such as 2.5 grams, 2 grams,1.5 grams, or even 1 gram.

The microcapsules disposed on the surface of the charcoal can be, asmentioned above, contained in a binder. Such a binder can be present inthe coating slurry and is normally a flammable material. The binder canbe hydrophilic or hydrophobic. When hydrophilic, the binder can bepresent in the aqueous phase of an oil-in-water emulsion polymerizationmethod for forming the microcapsules. Examples of such binders includepolyvinyl alcohol.

In disposing the microcapsules on the surface of the charcoal, asub-coating can be applied between the charcoal and the microcapsules ifdesired. Such a sub-coating can be used to improve adhesion of themicrocapsules to the charcoal, whether dispersed in a binder or not,and/or to improve flammability.

Additional ingredients can be added to the microcapsules, the charcoal,and the optional binder-containing layer. For example, the microcapsulesmay contain further ingredients within the core such as a colorant orflavor/odor enhancer. Usually, however, it is preferred that onlyignitable material and residues from the encapsulation process arewithin the core. The charcoal may be impregnated with ignitable materialand then the microcapsules disposed thereon. When the microcapsules aredispersed in a binder-containing layer, the layer may contain additionaladditives such as colorants, additional igniter agents, etc. In oneembodiment, a colorant is added to the coating slurry so that thecharcoal is colored. The charcoal may be coated on only one side but thecolor will indicate to the user which side to light; e.g., which sidecontains the microencapsulated ignitable material. In anotherembodiment, two different coating slurries are formed having differentcolors and the charcoal is partially coated in each slurry.

The invention is further illustrated by the following non-limitingexample.

Example

Materials

Oil 1 Commercial charcoal lighter fluid 122.69 g (petroleum distillate)2,2′-azobis(2,4-dimethylpentanenitrile) 0.65 g (Vazo 52-DuPont,Wilmington DE) 2,2′-azobis(2-methylbutyronitrile) 0.42 g (Vazo67-DuPont, Wilmington, DE)

Oil 2 Commercial charcoal lighter fluid 40.90 g (petroleum distillate)2-(tert-butylamino) ethyl methacrylate 0.55 g TBAEMA (Sigma-Aldrich, St.Louis, MO) 2-carboxyethyl acrylate (Beta 0.42 g C-Bimax Inc., Glen Rock,PA) Ethylene dimethacrylate (SR297- 21.42 g Sartomer Company, Inc.,Exton, PA)

Water Phase Polyvinyl alcohol (Celvol 540- 30.51 g Celanese Ltd.,Pasadena, TX) Water 368.70 g (4,4′-azobis(4-cyanovaleric) acid (Vazo1.27 g V-501-Du Pont, Wilmington, DE) 20% NaOH (Hydrite Chemical Co.1.62 g Brookfield, WI)

Process

Oil 1 Preparation

Components are combined at room temperature and stirred until insolution.

Oil 2 Preparation

Combine all components except SR297 and stir at room temperature. SR297is added later in the process.

Water Phase preparation

Combine all components and stir at room temperature until solution.

Procedure

The Vazos are dissolved in Oil 1, and the solution added to a jacketedstainless steel beaker with nitrogen blanket and heated to 35° C. whileagitating. Once Oil 1 is at 35° C., the solution is then graduallyheated to 75° C. and thereafter cooled to 55° C. Before Oil 1 reaches55° C., SR297 is added to the remaining, already combined Oil 2components. When Oil 1 reaches 55° C., Oil 2 is added to Oil 1. TheWater Phase is added and an oil-in-water emulsion is formed by millingat high shear (3500 rpm) until target drop size is achieved. Afteremulsification, the high shear blade is replaced with an agitator andmixed so as to keep the emulsion agitated. After the oils have beencombined, the emulsion is heated in stages over 13 hours to 75° C., to90° C. being held at 90° C. for 8 hours. The nitrogen blanket is turnedoff, and the coating material slurry allowed to cool to roomtemperature.

Briquette Coating Process

A charcoal briquette is held by tongs, and dipped into finished coatingmaterial slurry. The charcoal can be immersed or partially dipped toeffect partial coating. The briquette is then removed from the slurry,placed on a drying rack, and allowed to dry at room temperature or in a35° C. oven until dry. This process can be repeated if a higher amountof capsule coating is desired.

Each of the patents mentioned above is incorporated herein by reference.The invention having been described it will be obvious that the same maybe varied in many ways and all such modifications are contemplated asbeing within the scope of the invention as defined by the followingclaims.

1. A charcoal composition, comprising charcoal and microcapsulesdisposed on the surface thereof or within the charcoal composition,wherein said microcapsules contain an ignitable material.
 2. Thecharcoal composition according to claim 1, wherein said microcapsuleshave a median size within the range of 1 to 30 microns.
 3. The charcoalcomposition according to claim 1, wherein said ignitable materialcomprises at least one hydrocarbon, at least one alcohol, orcombinations thereof.
 4. The charcoal composition according to claim 3,wherein said ignitable material is a liquid at room temperature.
 5. Thecharcoal composition according to claim 3, wherein said ignitablecomposition comprises C5 to C13 alkanes.
 6. The charcoal according toclaim 3, wherein said ignitable material contains a C1-C13 alcohol. 7.The charcoal composition according to claim 1, wherein saidmicrocapsules have a wall comprising a polyacrylate, gelatin, ormelamine-formaldehyde.
 8. The charcoal composition according to claim 7,wherein said microcapsules have a wall comprising polyacrylate.
 9. Thecharcoal composition according to claim 1, wherein said microcapsuleshave an aspect ratio of core to wall such that the cores are at least70% by weight of said microcapsules.
 10. The charcoal compositionaccording to claim 9, wherein said cores are 80 to 95% by weight of saidmicrocapsules.
 11. The charcoal composition according to claim 1,wherein said microcapsules are contained in a coating layer on saidcharcoal.
 12. The charcoal composition according to claim 11, whereinsaid coating layer further comprises a binder.
 13. The charcoalcomposition according to claim 1, wherein said microcapsules provide theignitable material in an amount of 2% to 25% based on the weight of thecharcoal.
 14. The charcoal composition according to claim 1, whereinsaid charcoal is in the form of a briquette.
 15. The charcoalcomposition according to claim 14, wherein said microcapsules provide0.5 g to 7 g of the ignitable material to the briquette.
 16. A processfor making a charcoal composition, which comprises: (a) coating charcoalwith a slurry comprising a liquid having microcapsules dispersedtherein, said microcapsules containing an ignitable material, to form awet coated charcoal; and (b) drying said wet coated charcoal to formcharcoal having said microcapsules disposed on the surface thereof 17.The process according to claim 16, wherein said charcoal is in the formof a briquette.
 18. The process according to claim 17, wherein saidslurry liquid contains water and polyvinyl alcohol and said drying stepremoves substantially the water from the wet coated charcoal to form acoating layer of microcapsules dispersed in a polyvinyl alcohol binder.